Field of the Invention
The present invention relates to an optimized design method for manufacturing a Fresnel grating.
Related Arts
In recent years, as application of a spectrometer to fields such as bio-medical, environmental monitoring and surveillance, agricultural science and technology, and industrial process monitoring is becoming wider, a conventional large spectrometers severely limits the application to these fields due to a huge volume and a bulky shape. Therefore, to develop a portable miniature spectrometer has an important realistic meaning. In the current phase, a Czerny-Turner optical system and an optical system that uses a flat field concave grating is used in a core optical splitting system with a miniature spectrum; however, the Czerny-Turner optical system uses too many optical components, including a collimating lens, a grating, and a focusing lens, and therefore the system has disadvantages such as being difficult to be installed and being poor in stability. The optical system that uses a flat field concave grating uses one optical component, that is, a concave grating, which implements functions of the collimating lens, the grating, and the focusing lens, making a huge contribution to simplify the optical system. However, the flat field concave grating has a complex manufacturing process, and is difficult to be produced in large quantities. In addition, the manufacturing difficulty for glitter in the concave grating is very high, which also limits the diffraction efficiency of the grating.
In this way, a new-type Fresnel grating optical system is put forward. A Fresnel grating is a spectrum optical splitting device that is formed by combining a Fresnel surface and a grating, and it has all roles of collimating, optical splitting, and focusing. The Fresnel grating may be a plane grating, which has a simple manufacturing process, and is easy to be produced in large quantities, so that costs of a spectrometer can be effectively reduced. However, due to complexity and multiplicity of the Fresnel surface, a difficult problem exists in optimization of a structure of the Fresnel grating.